The invention relates to the field of peritoneal dialysis, so-called PD, and in particular to automatic peritoneal dialysis, so-called APD. A problem with peritoneal dialysis is loss of protein, particularly albumin. More particularly, the invention relates to a method and an apparatus for preventing protein loss with PD.
Peritoneal dialysis means that dialysis occurs by using one of the body""s own membranes in the peritoneal cavity, the peritoneal membrane. A PD solution is placed in the peritoneal cavity inside the peritoneal membrane by means of a catheter which passes through the skin and into the peritoneal cavity. Slightly more than two liters of fluid can often be placed in the peritoneal cavity without the patient feeling any great discomfort.
The most common form of PD today is CAPD, continuous ambulatory peritoneal dialysis. With CAPD, a set of bags is used which are coupled to the patient""s catheter, in order, with the aid of gravity, to drain the spent PD solution from the patient""s peritoneal cavity into a waste bag and to add new PD solution to the patient from a sterile storage bag.
With APD, a machine is used, a so-called cycler, for achieving the necessary flows into and out of the patient. The machine transports PD solution from storage bags to the cycler, where it is heated, and further to the patient, and transports the PD solution from the patient to the cycler and further to a waste receiver. The cycler is provided with a measurement device which monitors the flows into and out of the patient. APD can be used during the night and may be more effective than CAPD. With APD, the patient avoids heavy lifting since the PD solutions do not need to be hung up in a high position which is required with CAPD.
One complication with dialysis is protein loss. The patient often has a low amount of protein in the blood already long before the treatment starts. The dialysis treatment brings about additional losses of protein. A low protein content in a patient is a risk factor which is coupled to high morbidity and mortality with hemodialysis.
In a normal healthy patient, the peritoneal cavity contains about 200 ml of a solution with a composition which is similar to blood plasma. This liquid contains proteins such as albumin and immunoglobins in a predetermined concentration. The concentration of albumin (20-30 g/l)in the peritoneal cavity is made up of an inward flow from the blood path to the peritoneal cavity, which normally occurs through the peritoneal membrane, and an outflow of albumin via the lymph pathways. The composition of the fluid varies from person to person.
With peritoneal dialysis, the protein content in the fluid inside the peritoneal cavity is diluted and its colloid osmotic pressure is thereby lowered, that pressure being however replaced by a high glucose amount which creates the necessary crystal osmotic gradient in order to remove fluid from the patient.
The fluid which is present in the peritoneal cavity during peritoneal dialysis is thus different than that which is normally present in the peritoneal cavity of healthy persons in at least two respects, namely a high glucose content and a low protein content. There is reason to believe that both characteristics may lead to complications and it would be desirable to raise the content of protein in order thereby to be able to reduce the glucose content.
It is known that the increased exposure to glucose in a PD patient may lead to hyperinsulinemia with associated risk of cardio-vascular disease.
Additionally, a daily loss of albumin and other protein substances of about 5 g-25 g occurs by the spent dialysis solution being led to a waste receiver or to a waste bag which is later discarded.
The abnormally low content of immunoglobulins which are present in the peritoneal cavity during PD probably contributes to increased risk of peritonitis.
Protein has a buffer capacity, and a reduced content of proteins in the peritoneal cavity means that a PD solution with low pH is neutralised to a lesser extent, or more slowly, during the fill of the peritoneal cavity.
With PD it has previously been proposed to circulate the PD solution in a closed circuit, whereby protein losses and losses of other substances are avoided. The PD solution is allowed to pass on one side of a membrane in a dialyser where the PD solution is regenerated by dialysis against an outer dialysis solution whereby waste products are removed, see U.S. Pat. Nos. 4,338,190, 5,141,493 and 4,276,175.
In WO 97/47337, the D solution is regenerated by means of a semi-permeable membrane in order to raise the osmotic effect of the proteins within the PD solution and to use these proteins as osmotic means. If necessary, other components such as electrolytes or amino acids are added.
These known constructions attack the problem of protein loss. However these known constructions are difficult to carry out in practice.
They require use of a double-lumen-catheter with simultaneous inlet and outlet to the peritoneal cavity, in order to obtain a continuous flow. It can be difficult to make such a continuous flow be effective since it easily happens that the PD solution passes more or less straight through between the inlet and the outlet without coming into close contact with the peritoneal membrane.
Another problem is that a circulation pump is required in order to drive the PD solution in the intended circuits. The pump has to have the capacity to achieve the required circulation. If any component in the circuit should have a fault, such as a hole in a semi-permeable membrane, there is a risk that the patient will be subjected to much too large a pressure from the pump, being either an under-pressure or an over-pressure.
A third problem is that the aforementioned constructions are often expensive since they need many and expensive components, both in the required cycler and for disposable components.
A first object of the present invention is to achieve a method and an apparatus which prevents protein loss with peritoneal dialysis, particularly with APD.
A second object of the invention is to achieve a method which is such that it can be used with a conventional cycler, whereby the cost can be kept low.
A third object of the invention is to achieve a method and an apparatus which do not risk subjecting the patient to too high a pressure even if a fault should occur in the disposable products which are used.
A fourth object of the invention is to achieve a method and an apparatus which can be used with a normal catheter having only one passage.
A fifth object of the invention is to achieve a method and an apparatus which prevents protein loss and in which dialysis solution is continuously or intermittently supplied from a source of PD solution and spent PD solution is continuously or intermittently removed from the patient to a waste receiver.
In order to meet these objects, a method is provided according to the invention for preventing protein loss with peritoneal dialysis, comprising draining spent PD solution from a patient to a drain bag, passing the spent PD solution in the drain bag through a filter device for enrichment of a protein-rich fraction, and supplying the protein-rich fraction to a fresh PD solution intended to be supplied to the patient.
The protein-rich fraction or filter retentate is suitably collected in a protein bag for later supply to the fresh PD solution, whilst the protein-lean fraction or filtrate passing through the filter is sent to a waste receiver.
The protein bag may be positioned at a predetermined height above the filter in order to achieve a hydraulic back-pressure.
The invention also relates to an apparatus for carrying out the aforementioned method. The apparatus includes a device for draining spent PD solution from a patient to a drain bag, a device for passing spent PD solution in the drain bag through a filter device for enrichment of a protein-rich fraction, and a device for supplying the protein-rich fraction to a fresh PD solution intended to be supplied to the patient.
The apparatus also suitably comprises a device for collecting the protein-rich fraction in a protein bag for later supply to the fresh PD solution, and a device for sending the protein-lean fraction passing through the filter to a waste receiver.